West. N. W. East. S. W. South, N. E. N.S. E. Days 45 26 23 22 20 19 14 12 West. N. W. East. S. W. South. N. E. N.S.E. Days 27 27 19 24 22 15 32 18 245. The west wind blows during the whole year seventy-two days; the north-west fiftythree; the south-west and north forty-six days each. During summer it is calm for forty-one days, and during winter for twenty-one. In Norway the most frequent winds are the south, the south-west, and south-east. The wind at Bergen is seldom directly west, but generally south-west or south-east; a north-west, and especially a north-east wind, are but att.e known there. 246. From the whole of these facts, it appears that the most frequent winds on the south coasts of Europe are the north, the north-east, and north-west; and, on the western-coast, the south west that in the interior parts which lie most contiguous to the Atlantic Ocean, south-west winds are also most frequent; but that easterly winds prevail in Germany. Westerly winds are also most frequent on the north-east coast of Asia. 247. It is probable that the winds are more constant in the south temperate zone, which is in a great measure covered with water, than in the north temperate zone, where their direction must be frequently interrupted and altered by mountains and other causes. is also the north-west, and next to it is the west. 250. Thus it appears that the trade-winds sometimes extend farther into the south temperate zone than their usual limits, particularly during summer; that beyond their influence the winds are commonly westerly, and that they blow in the following order: north-west, southwest, west. 251. Thus have we finished the history of the direction of the winds. In the torrid zone they blow constantly from the north-east on the north side of the equator, and from the south-east on the south side of it. In the north temperate zone they blow most frequently from the southwest; in the south temperate zone from the north-west, changing, however, frequently to all points of the compass, and in the north temperate zone blowing particularly during spring from the north-east. 252. The phenomena that result from the vibration of elastic aeriform bodies usually form an important part of the science of pneumatics; we have, however, already furnished the reader with a general treatise on this subject under its proper head, and we now advert to it only to complete that branch of acoustics which could not have been understood without a reference to the principles of optics. We may commence with the airalogy which is usually supposed to exist between light and sound. On this subject we find Dr. Young full and interesting. 253. Ever since the publication of Sir Isaac Newton's incomparable writings, his doctrines of the emanation of particles of light from lucid substances, and of the formal pre-existence of colored rays in white light, have been almost universally admitted in this country, and but little opposed in others. Leonard Euler indeed, in several of his works, has advanced some powerful objections against them, but not sufficiently powerful to justify the dogmatical reprobation with which he treats them; and he has left that system of an ethereal vibration, which after Huygens and some others he adopted, equally liable to be attacked on many weak sides. Without pretending to decide positively 248. M. de la Bailie, who was sent thither by on the controversy, it is conceived that some the French king to make astronomical observa- considerations may be brought forwards, which tions, informs us that at the Cape of Good may tend to diminish the weight of objections Hope the main winds are the south-east and to a theory similar to the Huygenian, There are north-west; that other winds seldom last longer also one or two difficulties in the Newtonian than a few hours; and that the east and north- system which have been little observed. The east winds blow very seldom. The south-east first is, the uniform velocity with which light is wind blows in most months of the year, but supposed to be projected from all luminous bochiefly from October to April; the north-west dies, in consequence of heat, or otherwise. How prevails during the other six months, bringing happens it that, whether the projecting force is along with it rain, and tempests, and hurricanes. the slightest transmission of electricity, the fricBetween the Cape of Good Hope and New Hol- tion of two pebbles, the lowest degree of visible land the winds are commonly westerly, and ignition, the white heat of a wind furnace, or the blow in the following order: north-west, south-intense heat of the sun itself, these wonderful west, west north. 249. In the great South Sea, from lat. 30° to 40° S. the south-east trade-wind blows most frequently, especially when the sun approaches the tropic of Capricorn; the wind next to it in frequency is the north-west, and next to that is the south-west. From S. lat. 40° to 50° the prevailing wind is the north-west, and next the south west. From 50 to 60° the most frequent wind corpuscles are always propelled with one uniform velocity? For, if they differed in velocity, that difference ought to produce a different refraction. But a still more insuperable difficulty seems to occur in the partial reflection from every refracting surface. Why, of the same kind of rays, in every circumstance precisely similar, some should always be reflected, and others 'ransmitted, appears in this system to be wholly inexplicable. That a medium resembling, in many properties, that which has been denominated ether, does really exist, is undeniably proved by the phenomena of electricity; and the arguments against the existence of such an ether throughout the universe have been pretty sufficiently answered by Euler. The rapid transmission of the electrical shock shows that the electric medium is possessed of an elasticity as great as is necessary to be supposed for the propagation of light. Whether the electric ether is to be considered as the same with the luminous ether, if such a fluid exists, may perhaps at some future time be discovered by experiment. The uniformity of the motion of light in the same medium, which is a difficulty in the Newtonian theory, favors the admission of the Huygenian; as all impressions are known to be transmitted through an elastic fluid with the same velocity. It has been already shown that sound, in all probability, has very little tendency to diverge in a medium so highly elastic as the luminous ether must be supposed to be, the tendency to diverge may be considered as infinitely small, and the grand objection to the system of vibration will be removed. It is not absolutely certain that the white line visible in all directions on the edge of a knife, in the experiments of Newton and of Mr. Jordan, was not partly occasioned by the tendency of light to diverge. Euler's hypothesis, of the transmission of light by an agitation of the particles of the refracting media themselves, is liable to strong objections; according to this supposition the refraction of the rays of light, on entering the atmosphere from the pure ether which he describes, ought to be a million times greater than it is. For explaining the phenomena of partial and total reflection, refraction, and inflection, nothing more is necessary than to suppose all refracting media to retain, by their attraction, a greater or less quantity of the luminous ether, so as to make its density greater than that which it possesses in a vacuum, without increasing its elasticity; and that light is a propagation of an impulse communicated to this ether by luminous bodies: whether this impulse is produced by a partial emanation of the ether, or by vibrations of the particles of the body, and whether these vibrations are, as Euler supposed, of various and irregular magnitudes, or whether they are uniform, and comparatively large, remains to be hereafter determined. Now, as the direction of an impulse transmitted through a fluid, depends on that of the particles in synchronous motion, to which it is always perpendicular, whatever alters the direction of the pulse will inflect the ray of light. If a smaller elastic body strike against against a larger one, it is well known that the smaller is reflected more or less powerfully, according to the difference of their magnitudes: thus, there is always a reflection when the rays of light pass from a rarer to a denser stratum of ether; and frequently an echo when a sound strikes against a cloud. A greater body striking a smaller one propels it, without losing all its motion; thus the particles of a denser stratum of ether do not impart the whole of their motion to a rarer, but, in their effort to proceed, they are recalled by the attraction of the refracting substance with equal force; and thus a reflection is always secondarily produced, when the rays of light pass from a denser to a rarer stratum. The repulsion of inflected rays has been very ably controverted by Mr. Jordan, the ingenious author of a late publication on the Inflection of Light. It has already been conjectured by Euler that the colors of light consist in the different frequency of the vibrations of the luminous ether: it does not appear that he has supported this opinion by any argument; but it is strongly confirmed by the analogy between the colors of a thin plate and the sounds of a series of organ pipes. The phenomena of the colors of thin plates require, in the Newtonian system, a very complicated supposition, of an ether anticipating by its motion the velocity of the corpuscles of light, and thus producing the fits of transmission and reflection; and even this supposition does not much assist the explanation. It appears, from the accurate analysis of the phenomena which Newton has given, and which has by no means been superseded by any later observations, that the same color recurs whenever the thickness answers to the terms of an arithmetical progression. Now this is precisely similar to the production of the same sound by means of a uniform blast, from organ-pipes which are different multiples of the same length. Supposing white light to be a continued impulse or stream of luminous ether, it may be conceived to act on the plates as a blast of air does on the organ-pipes, and to produce vibrations regulated in frequency by the length of the lines which are terminated by the two refracting surfaces. It may be objected that, to complete the analogy, there should be tubes, to answer to the organ-pipes: but the tube of an organ-pipe is only necessary to prevent the divergence of the impression, and in light there is little or no tendency to diverge; and, indeed, in the case of a resonant passage, the air is not prevented from becoming sonorous by the liberty of lateral motion. It would seem that the determination of a portion of the track of a ray of light through any homogeneous stratum of ether is sufficient to establish a length as a basis for colorific vibrations. In inflections, the length of the track of a ray of light through the inflecting atmosphere may determine its vibrations: but, in this case, as it is probable that there is a reflection from every part of the surface of the surrounding atmosphere, contributing to the appearance of the white line in every direction, in the experiments already mentioned, so it is possible that there may be some second reflection at the immediate surface of the body itself, and that, by mutual reflections between these two surfaces, something like the anguiform motion suspected by Newton may really take place; and then the analogy to the colors of thin plates will be still stronger. A mixture of vibrations, of all possible frequencies, may easily destroy the peculiar nature of each, and concur in a general effect of white light. The greatest difficulty in this system is, to explain the different degree of refraction of differently colored light, and the separation of white light in refraction: yet, considering how imper fect the theory of elastic fluids still remains, it cannot be expected that every circumstance should at once be clearly elucidated. It may hereafter be considered how far the excellent experiments of count Rumford, which tend very greatly to weaken the evidence of the modern doctrine of heat, may be more or less favorable to one or the other system of light and colors. 254. Mr. Wheatstone's experiments are of a very novel and curious character, and as such must be next adverted to. 255. The application of the principles of science to ornamental and amusing purposes contributes, in a great degree, to render thein extensively popular; for the exhibition of striking experiments induces the observer to investigate their causes with additional interest, and enables him more permanently to remember their effects. 256. But the kaleidophone possesses higher claims to attention; for it exemplifies an interesting series of natural phenomena, and renders obvious to the common observer what has hitherto been confined to the calculations of the mathematician; it presents another proof that, however remote from common observation the operations of nature may be, the most beautiful order and symmetry preval through all. 257. In the property of creating beautiful forms,' the kaleidophone resembles the celebrated invention of Dr. Brewster, from which its name is modified; but to the instrument itself, and its mode of action, it is almost superfluous to say there is no similarity. Previously to entering into an explanation of its construction and effects, the following brief summary may suffice to give a general idea of the nature of the experiments it is intended to illustrate. 258. These experiments principally consist in subjecting to ocular demonstration the orbits or paths described by the points of greatest excurtion in vibrating rods, which in the most frequent cases, those of the combinations of different modes of vibration, assume the most diversified and elegant curvilinear forms. We are indebted to Dr. T. Young for the first observation of these phenomena; the following account of his experiments is quoted from the Philosophical Transactions for 1800. Take one of the lowest strings of a square piano-forte, round which a fine silvered wire is wound in a spiral form; contract the light of a window, so that when the eye is placed in a proper position, the image of the light may appear small, bright, and well defined, on each of the convolutions of the wire. Let the chord be now made to vibrate, and the luminous point will delineate its path like a burning coal whirled round, and will present to the eye a line of light, which, by the assistance of a microscope, may be very accurately observed. According to the different ways by which the wire is put in motion, the form of this path is no less diversified and amusing than the multifarious forms of the quiescent lines of vibrating plates discovered by professor Chladni; and it is, indeed, in one respect even more interesting, as it appears to be more within the reach of mathematical calculation to determine it,' 259. The extremely limited extent of the excursions of a vibrating chord prevents its motion from being distinctly observed by the naked eye, but as the rods employed in the present experiments can extend their excursions to nearly two inches, and as the means employed greatly increase the intensity of the light, the phenomena are exhibited in a far more evident manner. The entire track of each orbit is rendered simultaneously visible by causing it to be delineated by a brilliantly luminous point; and, the figure being completed in less time than the duration of the visual impression, the whole orbit appears as a continued line of light. As, besides the changes which result from the combinations of the primitive with the higher modes of vibration, the figures of the orbits are affected by the form of the rod, by the extent of the excursions of the vibrations, by the mode of producing the motions, and by many other circumstances, a great variety of pleasing and regular forms is obtained. This variety is also enhanced by giving the same motions to a number of symmetrically disposed luminous points, the mutual intersections of the orbits of which produce innumerable elegant forms; and the appearances may be still more variegated by occasionally causing these points to reflect differently-colored lights. 260. The apparatus for exhibiting these experiments consists of a circular board about nine inches in diameter, into which are perpendicularly fixed, at equal distances from the circumference and from each other, three steel rods, each about a foot in length. The first rod is cylindrical, about one-tenth of an inch in diameter, and is surmounted by a spherical bead. The only beads well adapted for this purpose are made of extremely thin glass silvered on the interior surface, and about onesixth of an inch in diameter; they are to be obtained at the shops under the name of steel beads. The protuberances at the apertures must be removed or blackened, otherwise the reflections from them will render the images confused. To produce the colored tracks, these beads must be coated with transparent colors, such as are ordinarily used for painting on glass; the light will then be reflected through the colored surface; but, in beads made of colored glass, the reflection being made from the external surface, shows only white light. The bead is cemented into a small brass cup screwed to the top of the wire, which concentrates and reflects the light which falls upon it. The second is a similar rod, upon the upper extremity of which is placed a plate moving on a joint, so that its plane may be rendered either horizontal, oblique, or perdendicular; this plate is adapted to the recep tion of the objects, which consist of beads differently colored and arranged on pieces of black card in symmetrical forms. The third is a foursided prismatic rod, and a similar plate is attached to its extremity for the reception of the same objects. Another rod is fixed at the centre of the board; this is bent to a right angle, and is furnished with a bead similarly to the firstmentioned rod. A small nut and screw are fixed to the board near the lower end of the first rød, in order by pressing upon it to render occasionally its rigidity unequal. A hammer, softened by a leather covering, is employed to strike the rods; and a violin-bow is necessary to produce some varieties of effect. 261. We may now proceed to describe the different appearances which the rods present when in action, and to give directions for the production of the different effects, following the order in which the rods have been previously mentioned. 262. On causing the straight rod to vibrate, so that its lowest sound be produced. The most simple mode of vibration of a rod vibrating transversely, when one of its extremities is fixed and the other is free, is that in which the entire rod makes its vibrations alternately on each side of the axis, which is nowhere intersected by the curve, but only touched at the fixed end. This gives the gravest sound which can be produced from the rod. In the other modes of vibration the axis is intersected by the curve one, two, three, or more times. The best means to command the production of these sounds is to touch a node of vibration lightly with the finger, and to put a vibrating part in motion by a violinbow. In the second sound, the number of vibrations is to that of the first as 52: 23, or 25: 4; the difference of the sounds is, therefore, two octaves and an augmented fifth. Separating the first sound from the series, the number of the vibrations of all the others will be to one another as the squares of the numbers 3, 5, 7, 9, &c.; the third, in which there are three nodes, will therefore exceed the second by an octave and an augmented fourth; in the fourth the acuteness will be augmented by nearly an octave; in the fifth by nearly a major sixth, &c. To reduce to the same pitch all the proportions of the sounds which such a rod is capable of producing, Mr. W. regards the sound corresponding with the most simple motion as the C one octave lower than the lowest of the piano-forte; the proportions of the sound will then be The possible series of sounds, regarding the fundamental as unity, will therefore be-1, 64, 17, 31, 561, &c.; or expressed in integral numbers -36, 225, 625, 1225, 2025, &c.- Chladni, Traité d'Acoustique, p. 91. As it is seldom that the motions of a cylindrical rod can be confined to a plane, the vibrations will almost alIways be combined with a circular motion. When the pressure on the fixed end is exerted on two opposite points, and the rod put in motion in the direction of the pressure, the following progression in the changes of form will be distinctly observed: the track will commence as a line, and almost immediately open into an ellipse, the lesser axis of which will gradually extend as the larger axis diminishes, until it becomes a circle; what was before the less will then become the larger axis, and thus the motions will alternate until, from their decreasing magnitudes, they cease to be visible. In the case just described the ellipses make a right angle with each other; but by altering the direction of the motion, so as to render it oblique to the direction of the pressure, they may be made to intersect under any required angle, and when this angle = 0 the motion will be merely vibratory. 263. Every single sound formed by the subdivisions of the rod will present similar appearances, but the excursions will be smaller as the sound is higher, or, which is the same thing, as the number of the vibrations increases. 264. In the most simple case of the co-existence of two sounds, shown by putting the entire rod in motion, and producing also a higher sound by the friction of a bow; the original figure will appear waved or indented, and, as unity is to the number of indentations, so will the number of vibrations in the lower sound be to the number in the higher sound. On varying the mode of excitation, by striking the rod in different parts and with different forces, very complicated and beautiful curvilinear forms may be obtained. 265. Placing the hand on the lower part of the rod, below the place at which it is excited, the excursions of the motions will rapidly decrease and exhibit spiral figures. 266. To obtain the figures with brilliancy and distinctness, a single light only should be employed, as that of the sun, a lamp, or a candle; rays of light proceeding from several points, as from a number of candles, or from the reflection of the clouds, occasion the track to be broad and indistinct; but double lights may be employed with effect, provided they be of equal intensity and symmetrically placed; each bead will then describe two similar figures. The appearances, in a bright sunshine, are remarkably vivid and brilliant. 267. Although very beautiful and varied forms may be produced from the motion of a single point, yet the compound figures, which are presented by objects formed by a number of points, offer appearances still more pleasing to the eye. 268. An object being placed horizontally on the plate of the second rod, and the rod being put in motion, the mutual intersections of the points each describing a similar figure, present to the eye complicated, yet symmetrical figures, resembling elegant specimens of engine-turning. 269. When the plate is horizontal, the figures are all in one plane, but if it be inclined or perpendicular, the curves being then made in parallel planes, gives the idea of a solid figure, and in some cases the appearances are particularly striking. 270. Complementary colors alone should be employed in the objects; for these, harmonising together, give greater pleasure to the eye than an injudicious combination of discordant tints: the intensities should be occasionally varied, and colorless light in'ermingled with the different shades. 271. When the prismatic rod is put in motion, in the direction of either of its sides, the points move only rectilineally; but, when the motion is applied in an oblique direction, a variety of compound curves is shown: this rod is principally employed to exhibit the optical phenomena which will be afterwards mentioned. 272. When a rod is straight, the curve produced by any point describing its motion is always in the same plane; but in a rod bent to any angle, the two parts moving most frequently in different directions, curves are produced whose parts do not lie in the same plane. A few trials will soon indicate the best way of applying the motion, so as to cause the two parts to vibrate in different directions. 273. When dark objects are substituted for luminous ones, their tracks become nearly invisible, and, from the onger duration of the visual impression at the limits of vibration, the images are multiplied in proportion to the number of points at which they are retarded. Place horizontally, on the second rod, a word printed or written on a piece of card; in the lowest mode of vibration, at the opposite limits of the excursions, two legible images of the word will be distinctly seen, and but an indistinct shade, occasioned by the tracks of the letters, will appear in the intermediate space: the vibratory motion is imperceptible to the eye; the images will, therefore, appear stationary in this respect, but the diminution of the excursions will cause them to approximate very slowly and gradually towards the centre: this diminution operates so gradually as to allow the images to superpose each other completely at each recurring vibration, without producing any intermingling or confusion. 274. On placing the object perpendicularly, the two images will appear in parallel planes, the furthest image appearing through the first apparent surface. Small pictures have a singular effect applied in this manner. 275. When other sounds co-exist with the fundamental, the images are multiplied, but they become fainter as their number increases: these multiplied images are equally visible whether the vibrations be rectilineal, elliptical, or cir cular. 276. As that property of vision which occasions the apparent duration in the same places of visible images, after the objects which excite them have changed their positions, has enabled us to submit to inspection the phenomena above described, it may not be irrelevant to subjoin a description of an apparatus which illustrates the transient duration of the impressions of light in a very evident manner. 277. At the back of a wooden frame, about six inches in height and breadth, and from one to three inches or more in depth, a circular plate of glass is placed, upon which a design is painted with transparent colors; at the front is placed, parallel to the glass, a circle of tin, covered on its exterior surface with white paper, and having the space between two adjacent radii cut out. This circle moves freely on its centre round an axis, supported by a bar in front, and is put into rapid and regular motion by the application of any mechanical principle proper for the pur pose; and a catch is so placed that, when the motion ceases, the aperture shall be concealed by the bar which supports the axis. 278. If a light be placed behind the transparent painting, and still better if it be concentrated by a lens, on making the circle revolve with rapidity, the whole of the picture will be rendered visible at one view, although but very limited portions are successively presented to the eye. 279. The intensity will differ in proportion to the excess of the transmitted light above that which falls in front of the circle; it will, therefore, increase the distinctness of the picture, to darken the latter as much as possible. 280. The next series of experiments by Mr. Wheatstone are of still greater importance than those already presented to our readers. They relate to the phonic molecular vibrations, and are incapable of abridgement. Mr. W. commences with an examination of what he terms linear phonics, and arranges them under two heads. 281. Transversal: making their oscillations at right angles to their axis. 1. Capable of tension, or variable rigidity: chords, or wires. 2. Permanently rigid: rods, fork, rings, &c. Longitudinal: making their oscillations in the direction of their axis. 1. Columns of aëriform fluids or liquids; cylindric and prismatic rods. Superficial phonics. 1. Capable of tension: extended membranes. 2. Permanently rigid: laminæ, bells, vases, &c. Solid phonics. 1. Volumes of aeriform fluids. The 282. The sensation of sound can be excited by any of these bodies when they oscillate with sufficient rapidity, either entire, or divided into any number of parts in equilibrium with each other. The laws of these subdivisions differ in the various phonics according to their form and mode of connexion or insulation; and the velocities of the oscillations, or degrees of tune, depend on the form, dimensions, mode of connexion, mode of division, and elasticity of the body employed. The points of division in linear phonics are called nodes, and the boundaries of the vibrating parts of elastic surfaces are termed nodal lines. parts of which the oscillatory portions have their greatest excursions are named centres of vibration; these are always at the greatest mean distances from the nodal points or lines. These mechanical oscillations are not however themselves the immediate causes of sound; they are but the agents in producing in the bodies themselves, and in other contiguous substances, isochronous vibration of certain particles varying in magnitude according to the degree of tune. convinced myself,' observes Mr. W., of this important fact by the following simple experiment: I took a plate of glass capable of vibrating in several different modes, and covered it with a layer of water; on causing it to vibrate by the action of a bow, a beautiful reticulated surface of vibrating particles commenced at the centres of the vibrating parts, and increased in dimensions as the excursions were made larger. When a more acute sound was produced the centres consequently became more numerous and the number of coexisting vibrating particles likewise increased, but their magnitudes proportion I |